Field of the Invention
The present invention relates to an image forming apparatus.
Description of the Related Art
As disclosed in Japanese Patent Application Laid-Open No. 2006-301108, a cleanerless system (a toner recycle system) has been conventionally proposed for image forming apparatuses such as electrophotographic apparatuses and electrostatic recording apparatuses in consideration of the simplification of an apparatus arrangement and the elimination of wastes. This cleanerless system does not use a dedicated drum cleaner as a surface cleaning unit after a transfer process with a photosensitive member in a transfer type image forming apparatus. This system cleans transfer residual toner on the photosensitive member after a transfer process by a developing device at the same time of developing (to be referred to as “developing with simultaneous cleaning” hereinafter) to remove the toner from the photosensitive member and collect the toner into the developing device to reuse it.
Developing with simultaneous cleaning is a method of collecting residual toner on a photosensitive member after a transfer process by using a fogging-removing bias (a fogging-removing potential difference Vback as the potential difference between a DC voltage applied to a developing device and the surface potential of the photosensitive member) at the time of developing after the next process. This method can eliminate waste toner and reduce a cumbersome manual operation for maintenance because the transfer residual toner is collected in the developing device and reused in the subsequent processes. In addition, this cleanerless arrangement provides a large advantage in terms of space, and hence allows a large reduction in the size of an image forming apparatus.
If there is residual charge on the photosensitive member, the surface potential of the photosensitive member is disturbed. For this reason, under a low-humidity environment, in particular, an image defect called a “drum positive ghost” sometimes occurs in the rotation cycle of the photosensitive member due to a charged potential difference on the photosensitive member. As disclosed in Japanese Patent Application Laid-Open No. 2001-142365, it is known that, in order to eliminate this “drum positive ghost”, it is effective to provide a so-called charge eliminating unit for charge eliminating the surface potential of the photosensitive member to a predetermined residual potential level by irradiating the surface of the photosensitive member with light before a charging process after a transfer process.
When a charge eliminating unit is mounted in an image forming apparatus having the cleanerless system, the inventors have studied and found that the following problem occurs.
More specifically, if the relationship between the light irradiation width of a charge eliminating unit and a transfer member width is improper in the rotation axis direction of a photosensitive member, a trouble sometimes occurs at an end portion of the photosensitive member.